Stent with self-deployable portion having wings of different lengths

ABSTRACT

The present invention provides methods and devices for placement of a stent in a bifurcation or ostial lesion. The stent comprises a main body and a flaring portion. The main body is designed to expand and support a main vessel of the bifurcation and defines a main body axis. The flaring portion is disposed on a side of the main body and is adapted to flare radially and offset the main body axis in response to expansion of the main body. The flaring portion comprises at least one distal wing and at least one proximal wing. Each wing is aligned along the main body axis. The at least one proximal wing is longer than the at least one distal wing, providing greater coverage of the proximal side of the side vessel than on the distal surface of the side vessel.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation-in-part application ofnon-provisional application Ser. No. 11/330,382 (Attorney Docket No.022246-000240US), entitled “Stent with Self-Deployable Portion” andfiled on Jan. 10, 2006, which is related to and claims the benefit ofthe following prior provisional applications: Nos. 60/740,935 (AttorneyDocket No. 022246-000230US), filed on Nov. 29, 2005; 60/712,949(Attorney Docket No. 022246-000220US), filed on Aug. 30, 2005;60/684,454 (Attorney Docket No. 022246-000210US), filed on May 24, 2005;and 60/643,062 (Attorney Docket No. 022246-000200US), filed on Jan. 10,2005. The full disclosures of the aforementioned applications areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to medical devices and more specificallyto medical devices used in the treatment of vascular stenoses at or neara bifurcation lesion.

Stenting is a common medical procedure mainly directed atrevascularization of stenotic vessels where a blocked artery is dilatedand a stent is placed in the artery to maintain vessel patency followingthe procedure. A stent is small mesh like tubular device, usuallyfabricated from metal, that can be coated with a drug or a polymercontaining a drug.

While stents are successful in treating a variety of lesions in thevascular system, their success is limited in the treatment ofbifurcation lesions and ostial lesions. Often, during stent placement inthe main vessel at a bifurcation lesion, the stent mesh blocks access tothe side branch thereby disrupting blood flow patterns and limitingblood flow to the side branch. Additionally, placing a stent in the sidebranch of a bifurcation lesion often results in the stent protrudinginto the main vessel which can later interfere with stent placement inthe main vessel as well as limiting branch vessel access.

In addition to acute problems such as long procedure time, complicationsfrom stents placed in bifurcation lesions can result due to the limitedside branch access along with the need to use conventional stentsagainst their intended design or labeled use. This can compromise longterm results resulting in a higher rate of restenosis as compared tostenting other lesions.

One method of using conventional stents in bifurcation lesions is todeliver a first stent to the main vessel followed by delivering a secondstent to the side branch through the struts of the main vessel stent.However, this procedure is difficult since the second stent can getcaught while passing through the first stent. Another commonly usedmethod is to place the side branch stent before the main vessel stent.In this case, there could be a gap between the two stents, andrestenosis often occurs in this gap. Alternatively, the gap may beeliminated by delivering the side branch stent with a portion protrudinginto the main vessel. In this case the protruding stent will be crushedduring delivery and expansion of the main vessel stent. Results ofcrushing the side branch stent are hard to predict and can lead toundesired deformation of the stent as well as dissection of the bloodvessel.

Drug eluting stents have demonstrated clinical success in the coronaryvessels but have failed so far to demonstrate similar success rates inbifurcation lesions. This outcome is attributed to the lack of metallicstent coverage in the gap between the main vessel stent and the sidebranch stent.

Conventional stent designs are well disclosed in the prior art. Thesedesigns comprise a number of different stent configurations andgeometries along with various coatings and materials for fabrication.Stainless steel and cobalt chromium alloys are commonly used for balloonexpandable stents while a nickel titanium alloy is typically employed inself-expanding stents. The use of self-expanding stents in the coronaryarteries is limited however, due to the need for accurate sizing andpositioning as well as because of the limited ability for post-deliverystent manipulation required for optimal stent positioning.

Attempts have been made to design a dedicated stent for bifurcationlesions. There is a need for ostial side branch support and local drugdelivery to the bifurcation area via a stent coating. However, currentsolutions suffer from a number of shortcomings such as high profilerelative to conventional stents, the need for a cumbersome deliverysystem to place the stent in the proper location and insufficientlyaccurate rotational positioning facing the side branch.

Stents with reduced profiles and improved flexibility have been designedand attempted using self-expanding stents made from superelasticmaterials (such as nickel titanium alloy). These stent devices do notrequire a balloon to expand the stent and therefore permit a reductionin profile. However, self-expanding stents are still difficult toposition and deliver to a target bifurcation site. Once expanded, thenickel titanium stents are not easily manipulated with a balloon nor ispost-delivery dilatation very effective.

Both balloon expandable stents and self-expanding stents for bifurcationlesions are limited in their ability to accommodate a wide range ofbifurcation angles. Self-expanding Nitinol strives to achieve itspre-set configuration and thus undesired gaps might be created betweenthe stent and the vessel wall after expansion. Also, currently availableballoon expandable stents are limited in their ability to adopt thelocal anatomical configuration.

To overcome this problem, a “kissing balloon” technique is often used.In this technique two angioplasty balloons are simultaneously inflatedin the main vessel and the side branch with the objective of obtaininggood wall apposition of the stents. This technique is currently the bestmethod available. However, the two balloons are inserted into the arteryover conventional metallic guidewires that affect the local geometry atthe bifurcation site and suppress the real bifurcation angle. Once theballoons and the wires are pulled out, the side branch angle is restoredto its original position and this can leave a gap between the stent andthe arterial wall.

For these reasons and others, the current treatment for bifurcationlesions is limited in the complexity of lesions that can be treated aswell as the long term clinical benefits provided to patients. At leastsome of these objectives will be met by the present invention.

BRIEF SUMMARY OF THE INVENTION

The present invention provides methods and devices for the placement ofa stent in a bifurcation or ostial lesion. The term “bifurcation” inthis patent includes all types of bifurcation lesions and lesions nearbifurcations in the vessels. The phrases “bifurcation ostium area” and“ostial lesion” apply to all types of lesions including those located ataorto-ostial and anastomosis sites.

A main body portion of a balloon expandable stent is designed to expandand support the main vessel while a flaring portion is designed to openinto and support a side branch vessel and/or bifurcation ostium area atleast partially in response to expansion of the main body. The term“flaring portion” used in this application refers to a portion of thestent that protrudes outwardly from the stent surface after the stenthas been expanded, i.e., it is no longer radially collapsed. Expansionof the flaring portion can be achieved with the use of a single balloondisposed in the main body of the stent and without the need for anadditional balloon that is placed in the flaring portion.

In a first aspect, embodiments of the present invention provide anexpandable stent for deployment at a vascular bifurcation. The vascularbifurcation has a side vessel branching from a main vessel, typically atan acute angle in a distal direction. The stent comprises a main bodyfor expansion into the main vessel and a flaring portion disposed on aside of a main body. The main body defines a main body axis. The flaringportion is adapted to flare radially and offset the main body axis inresponse to expansion of the main body into the main vessel. The flaringportion comprises at least one distal wing and at least one proximalwing. Each wing is aligned along the axis of the main body. The at leastone proximal wing is longer than the at least one distal wing.

In many embodiments, the at least one distal wing and the at least oneproximal wing are configured to open at different angles relative to theaxis of the main body when the flaring portion flares radially into theside branch vessel. The at least one proximal wing may be configured toopen to a greater angle relative to the main body than the at least onedistal wing.

In many embodiments, the stent further comprises at least one connectordisposed between the main body and the wings. The at least one connectordeforms in response to expansion of the main body to cause the wings toflare radially. The at least one distal wing and the at least oneproximal wing may each comprise a base and sides. The at least oneconnector may be disposed between the main body and the base of eachwing. As explained below, the at least one connector generally transfersdisplacement and expansion forces from the main body to the flaringportion during expansion of the main body. A radiopaque marker may bedisposed above the base and between the sides. The at least one distalwing and the at least one proximal wing may further comprise strutsextending from the sides of each wing. These struts provide coverage ofa side branch ostium when the wing is opened into the ostium.

The expandable stent may be balloon expandable or self-expanding. Theflaring portion may flare at an angle in the range from 10 to 150degrees relative to the main body axis when the main body is expanded.Flaring of the stent flaring portion in the present invention istypically achieved by a leverage mechanism, e.g., the connector. Theleverage mechanism is connected between the main body and the flaringportion and therefore, as the main body expands, the leverage mechanismis also displaced. This displacement and the corresponding expansionforces are then transferred from the main body during expansion alongthe leverage mechanism to the flaring portion. The leverage mechanismcan be a part of the stent pattern which is designed to deflect forcesand lift the side portion. The leverage mechanism can also be a portionof the main stent body or a portion of the side branch supportstructure.

Also, the flaring portion of the stent may comprise a proximal anddistal portion. The dimensions of the leverage mechanism may be modifiedto make it stiffer which permits greater transfer of force anddisplacement from the main body during expansion to the distal flaringportion. Therefore, the leverage mechanism deflects the distal portionmore than the proximal portion, thereby flaring the distal portion at agreater angle than the proximal portion.

The stent may also comprise a therapeutic agent disposed over at least aportion of the balloon expandable stent. The therapeutic agent may becoated on the stent or sequestered in a polymeric layer or other carrieradded to the stent. The therapeutic agent is delivered to at least aportion of the lesion, particularly the main vessel lesion, side branchlesion or side branch ostium and the therapeutic agent helps to reducerestenosis or inflammation post stent implantation.

Embodiments of the invention may also provide a stent delivery systemfor the expandable stent. The delivery system comprises the expandablestent and a delivery catheter. The delivery catheter comprises a shaftand an inflatable balloon. The shaft has a proximal end and a distalend. The inflatable balloon is disposed near the distal end of theshaft. The stent is disposed on the balloon with the distal end of thestent facing distally and a proximal end of the stent facing proximally.

In another aspect, embodiments of the invention provide a method fordeploying a stent at a vascular bifurcation. A main body of the stent ispositioned in a main vessel of the bifurcation. A distal wing and aproximal wing are opened from the main body into a side vessel of thebifurcation. The distal wing is shorter than the proximal wing so thatthere is greater coverage on a proximal surface of the side vessel bythe proximal wing than on the distal surface of the side vessel by thedistal wing.

The vascular bifurcation defines a proximal intersection angle betweenthe main vessel and the side vessel. The proximal wing may be opened toan angle corresponding to the proximal intersection angle. The vascularbifurcation also defines a transition zone or ostium between the mainvessel and the side vessel. The transition zone has a distal radius ofcurvature and the distal wing may be opened to an angle corresponding tothe distal radius of curvature.

In many embodiments, a side branch stent is positioned at the sidevessel. The side branch stent has a proximal end and a distal end. Theproximal end of the side branch stent is positioned adjacent thebifurcation. The side branch stent is expanded. Greater coverage on theproximal side of the vessel by the proximal wing than on the distal sideof the side vessel by the distal wing minimizes the gap between theproximal end of the side branch stent and the proximal and distal wingsof the main body.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a two-dimensional representation of a bifurcation stent,unrolled and flattened.

FIG. 2 shows the wings and connecting struts of the stent illustrated inFIG. 1.

FIG. 3 shows the bifurcation stent of FIG. 1 mounted on a balloon.

FIGS. 4-6 show the bifurcation stent at the bifurcation site before,during and after expansion.

FIG. 7 shows a two-dimensional representation of another bifurcationstent design, unrolled and flattened.

FIG. 8 shows radiopaque markers on the stent.

FIG. 8 a shows a two-dimensional representation of another bifurcationstent design lengthened with additional connector struts and with fourradiopaque markers.

FIG. 9 shows the mid-stent area of a bifurcation stent first to expand.

FIG. 10 shows a two-dimensional representation of an ostial stent,unrolled and flattened.

FIG. 11 shows an end portion of the stent in FIG. 10.

FIG. 12 shows the wings and connecting struts of the stent in FIG. 10.

FIG. 13 shows the ostial stent of FIG. 10 mounted on a balloon.

FIGS. 14-16 show an ostial stent at a bifurcation site before, duringand after expansion.

FIGS. 17-19 show an ostial stent at a bifurcation site with an anglebetween the branching vessels, before, during and after expansion.

FIG. 20 illustrates the angle of the flaring portion when disposed on aside of the main body.

FIG. 21 illustrates the angle of the flaring portion when disposed on anend of the main body.

FIG. 22 shows a two-dimensional representation of an unrolled andflattened bifurcation stent according to embodiments of the invention.

FIG. 22 a shows a side view of the expanded configuration of the stentof FIG. 22.

FIG. 22 b shows a perspective view of the expanded configuration of thestent of FIG. 22.

FIG. 23 shows the stent of FIG. 22 expanded into a bifurcation.

FIG. 24 shows the stent of FIG. 22 expanded into a bifurcation and aside branch stent expanded into the side branch vessel of thebifurcation.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is a balloon expandable stent for bifurcation andostial lesions. The word bifurcation in this patent includes all typesof bifurcation lesions and lesions near bifurcations in the vessels orostial lesions of all types including aorto-ostial and anastomosissites.

The stent has a tubular structure and comprises a main body that isballoon expandable and is capable of supporting a main vessel. It has aportion which flares at least partially into a side branch vessel andsupports the side branch ostium in response to expansion of the mainbody, without requiring an additional deployment balloon. An additionalballoon may be used to complete the deployment if needed.

An example of a bifurcation stent design 10 is shown in FIG. 1two-dimensionally, unrolled and flattened. Additional structuralfeatures of stent 10 are also illustrated in FIG. 2 and FIG. 3 shows thesame stent 10 mounted on a balloon 20. The stent 10 of FIG. 1 comprisesa structure 11 designed to radially expand and a connector 12 betweenthe radially expandable structure 11 and a flaring portion 13.

The radially expandable structure 11 is attached to both sides ofconnector 12 but does not necessarily form a circumferential ring. Thestructure 11 expands to support the main vessel while enabling theconnector 12 to open. Connector 12 is designed to have a geometricalpreference to deform outwardly rather than along the balloon surface.Once the expandable structure 11 expands and allows the connector 12 toopen, connector 12 is deflected outwardly.

Flaring portion 13 in this example comprises two wings 14 shown in FIG.2 that are interconnected with connecting struts 15 also shown in FIG.2. Additional wings may be added. Alternatively, the wings can bereplaced with meandering struts or any other strut design. Wings 14 areattached to connectors 12 and are deployed outwardly into the sidebranch when the connectors 12 deflect. The wings 14 shown in thisexample are symmetrical although each one can have a different size ordesign to allow better support of different bifurcation angles. Whenwings 14 are deployed, connecting struts 15 are pulled and may add morecoverage to the side branch ostium. The stent further comprises anotherradially expandable structure 16 shown in FIG. 1 that expands due toballoon inflation and supports the main vessel at the mid-stent area.This area can be designed with many different patterns to allow coverageof the main vessel.

FIGS. 4, 5 and 6 illustrate a bifurcation stent design 10 undergoing theexpansion process. FIG. 4 shows the stent 10 comprising a flaring region13 crimped over a balloon 20 in a blood vessel (BV), FIG. 5 shows thestent during expansion where the flaring portion 13 begins to flare inresponse to main body expansion and FIG. 6 shows the fully expandedstent with the flaring portion 13 extending into a side branch. FIG. 20shows α, the angle of the flaring portion relative to a central axis ofthe stent, which is in the range from 10 to 150 degrees, and the flaringportion is disposed on a side of the stent main body.

FIG. 7 shows another stent design 100 containing the similar structuralfeatures as previously described in FIGS. 1 and 2, but with dimensionsof structural features varied. In one embodiment the main stent body hasa different stiffness near its proximal and distal ends as compared tothe mid-stent region. This causes the center of the stent to expandfirst during deployment. Deployment of the center of the stent and theflaring portion can be achieved by altering the design of the balloon asshown in FIG. 9. One such example is a thinner balloon wall thicknesscloser to the center of the balloon 21. This pushes the flaring portionagainst the side branch ostium and it is deployed inside the sidebranch. Early expansion of the area near the flaring portion pushes thestent into place before deploying the flaring portion. The ballooncenter area design 21 can be controlled by the wall thickness, molddesign or thermal treatments of the polymer.

Varying the radial stiffness of different areas of the stent can beachieved in various ways. One option is to reduce the width of struts(e.g. 106) or their thickness in the stent area that is closest to theflaring portion. Optionally, longer struts may be used when lowerstiffness is desired. Another possible way is to increase the spacingbetween intersecting struts in areas where less radial stiffness isdesired (e.g. 101, 106).

In one embodiment the flaring portion structure 13 is designed to deployto a 90 degree angle. In another embodiment the flaring portion 13 isdesigned to be deployed to various pre-determined angles. In yet anotherembodiment the flaring portion 13 is tilted at varying angles to fit thebifurcation angle anatomy. An additional way to control the degree offlaring is by applying different inflation pressures to the main body ofthe balloon used for stent expansion.

In an alternative embodiment the stent is symmetrical and therefore bothwings 14 of the flaring portion 13 deploy in the same way and to thesame angle. Alternatively the stent 10 may not be symmetrical whichcauses the distal area of the flaring portion 13 to deploy at a greaterangle than the proximal area of the flaring portion 13. This can beachieved by transmitting less force on the connecting strut 12 at theproximal side which in turn deflects less and therefore lifts the wing14 to a lower angle.

An example of a way to transmit less force along the connecting strut 12is to make the radially expandable structure 11 weaker by using radiallyexpandable structure struts that are either longer, thinner or both.Similarly, stiffening connecting strut 12 on the distal side transmitsmore force and therefore deflects more thereby lifting the distal wing14 to a greater angle than the proximal wing. Alternatively, the wings14 may have different designs to allow for different properties and alsoto maximize other benefits such as selective drug delivery for example.

In another embodiment the stent may comprise radiopaque markers toassist accurate positioning of the stent. For example, in FIG. 8,radiopaque markers (30) fabricated from radiopaque materials such asgold, platinum, tantalum and the like, can be attached to the stent 10at different locations and can be viewed via fluoroscopy. FIG. 7 showsan example of a stent where the wings 114 of the flaring portion aredesigned to include a marker welded or otherwise attached to the stent.Preferred locations for these radiopaque markers are the wings 114 ofthe flaring portion. Having radiopaque markers placed on each of thewings 114 of the flaring portion will assist the physician indetermining where the flaring portion is positioned relative to the sidebranch before stent expansion as well as helping to position the stentaccurately. It will also enable the physician to see the flaring portiondeployed into the vessel side branch. This is advantageous because notonly does it help the physician to identify the side branch location butalso helps in placing a second stent or re-guidewiring the side branchfor post deployment treatments of the side branch area. Multipleradiopaque markers 308 may be attached to the flaring region in order tofurther enhance visibility as illustrated in FIG. 8 a, which shows fourradiopaque markers.

The stent can be made from biocompatible alloys such as stainless steel,cobalt chromium, titanium, nickel titanium alloys, niobium alloys or anyother material suitable for use in body implants. The stent may furtherinclude graft materials such as PTFE or polymer membranes. The stent maybe coated with an anti-inflammatory drug or other therapeutic agentswith or without a polymer. The use of self-expanding materials such asnickel titanium alloys is optional but not necessary for thefunctionality of the stent and the self-opening of the flaring portion.The stent can be made of resorbable or absorbable materials such asdifferent polymer formulations, magnesium alloys and other materialsthat are resorbable or absorbable under body conditions.

FIGS. 1 and 2 also illustrate another embodiment where the stent 10comprises three sections, a stent main body, a flaring portion 13 and anoptional leverage mechanism 12 or 15 connecting the main body and theflaring portion 13. The leverage mechanism 12 or 15 is designed toconnect the flaring portion 13 and the main body in a way such thatforces and displacement resulting from the partial expansion of thestent main body or the inflation of the main body balloon aretransferred and utilized to expand the flaring portion 13. The leveragemechanism 12 or 15 may be integrated with the design of the flaringportion 13 or the main body to help deploy the flaring portion 13 oncethe main body balloon is inflated, and can be fabricated in the same wayas the rest of the stent. For example, the entire stent patternincluding the side portion and the leverage mechanism may be laser cutfrom a tube.

In yet another embodiment of the invention the main body and the flaringportion share the same pattern or same pattern features. These twoportions of the stent are connected by a leverage mechanism withdifferent design features aimed to deploy the flaring portion byleveraging the geometrical changes and forces resulting from the mainbody expansion.

In another embodiment the flaring portion expansion occurs before thecompletion of the main body expansion. In this embodiment the sidebranch portion expansion helps the positioning and the alignment of thestent in the bifurcation area and allows the stent system to acquire theangle of the bifurcation and comply with the local anatomy.

In one embodiment the main body of the stent has more than a singlepattern. In this case the area of the stent that is close to the flaringportion has a different pattern than the areas of the stent that arefurther away from the flaring portion. The flaring portion may haveeither one of these patterns, a different pattern or no pattern at all.

In another embodiment the stent design allows the use of a deliverysystem with a single balloon without the need for additional means fordeploying the flaring portion. In this embodiment the profile of thesystem can be very low as compared to other bifurcation stent systemsand is typically lower than 0.06,″ preferably lower than 0.05″ andusually lower than 0.04″ which is a typical profile of conventionalstents not dedicated to bifurcation lesions. This low profile can beachieved due to the design of the stent and the automatically deployedflaring portion.

In another embodiment the stent can be coated with various coatingsincluding biocompatible oxide layers such as Ir oxide and the like, drugcontaining polymer coatings whether biodegradable or not, or drugmolecules, that can help reduce restenosis or minimize inflammation orimpact biological processes in the vessel with a beneficial outcome forthe patient.

In another embodiment the stent has a crimped configuration and anexpanded configuration. Usually in the crimped configuration the flaringportion is crimped with the stent but is not necessarily flush with thecrimped main stent body because struts in the flaring portion are notnecessarily flush with the crimped cylindrical surface of the stent.Sometimes the flaring portion can be crimped flush with the main body ofthe stent.

In yet another embodiment the stent has a crimped configuration and anexpanded configuration, whereas in the crimped configuration theproximal and distal ends of the stent are crimped to a smaller diameterthan the middle area of the stent.

Now turning to FIG. 8 a, another embodiment is illustrated withadditional radiopaque markers 308 in the flaring region and additionalstruts 310 which lengthen the stent body. FIG. 8 a illustrates abifurcation stent 300 two-dimensionally, unrolled and flattened. Thestent 300 of FIG. 8 a comprises a structure 301 designed to radiallyexpand and a connector 302 between the radially expandable structure 301and the flaring portion of the stent 305 and 313. The radiallyexpandable structure 301 is attached to one side of connector 302 butdoes not necessarily form a circumferential ring. The radiallyexpandable structure 301 expands to support the main vessel whileenabling connector 302 to open. Connector 302 is designed to have ageometrical preference to deform outwardly rather than along the balloonsurface. Once the expandable structure 301 expands and allows theconnector 302 to open, connector 302 is deflected outwardly.

A flaring portion of the stent comprises four wings 313 shown in FIG. 8a that are interconnected with connecting struts 305 which also flareand form part of the flaring portion. The wings 313 are attached toconnectors 302 and are deployed outwardly into the side branch when theconnectors 302 deflect. The wings 313 shown in this example aresymmetrical although each one can have a different size or design toallow better support of different bifurcation angles. When wings 313 aredeployed, connecting struts 305 are pulled inward and may add morecoverage to the side branch ostium.

Many delivery systems used to treat a bifurcation lesion have a sidesheath or a side branch guidewire that is placed in the side branch. Inmost cases the side sheath or side branch wire passes beneath theproximal side of the stent and exits through the side opening of thestent. In this embodiment, the side branch sheath or guidewire passesbeneath the proximal wing 313 and over the distal wing 313, which couldinterfere with distal wing deployment. Having four wings 313 isadvantageous because it creates a space in between the wings 313 andpermits the side branch catheter sheath or guidewire to be deployed intothe side branch without interfering with the wings 313.

The stent further comprises another radially expandable structure 306shown in FIG. 8 a that expands due to balloon inflation and supports themain vessel at the mid-stent area. This area can be designed with manydifferent patterns to allow for coverage of the main vessel.

Wings 313 have also been modified so that the stent may further compriseradiopaque markers to assist accurate positioning of the stent. Forexample, in FIG. 8 a, radiopaque markers 308 fabricated from radiopaquematerials such as gold, platinum, tantalum and the like, can be attachedto the stent 300 on the wings 313. The markers 308 may be attached tothe wings 313 by swaging, welding, or fusing, for example.

These four markers 308 are advantageous because they assist thephysician in viewing the flaring portion of the stent relative to theside branch before stent expansion as well as helping to position thestent more accurately. It will also enable the physician to see theflaring portion deployed into the vessel side branch. This isadvantageous because not only does it help the physician to identify theside branch location but also helps in placing a second stent orre-guidewiring the side branch for post deployment treatments of theside branch area. Additionally, having four markers on the stent enablesthe physician to determine the stent rotational orientation underfluoroscopy prior to stent deployment. When all four markers can bedetected, this is an indication that the stent side portion is eitherfacing the fluoroscopy screen or facing 180 degrees the other way. Thephysician can then torque the device and rotate it until only twomarkers are observed, indicating a side view, facing the ostiumdirection thereby confirming that the stent is properly aligned fordeployment.

The basic stent design described herein results in a relatively shortstent, typically six to eight millimeters long. Furthermore, thearchitecture of the stent can be designed to foreshorten during stentdeployment and cause movement of the struts toward the bifurcation arearesulting in more support to the bifurcation area.

In main vessels, the average lesion length is about 15 millimeters andmost lesions are in the range of 10 to 20 millimeters. Placing a shortstent at the bifurcation site often will require placing additionalstents both proximally and distally to the bifurcation stent. This isdifficult and undesirable since additional stents may entangle as theypass through the delivered stent. For this reason, it is desirable toadd length to the stent both proximally and distally and provide stentdesigns that vary in length typically between 10 and 20 millimeters. Anadditional lengthening structure can be added to the stent symmetricallyaround the side portion or may be added to proximal or distal sectionsof the stent. This additional structure can be designed with manydifferent geometries that support a vessel wall.

Many such geometries have been described previously. A common design forexample comprises rows of sinusoidal rings that are radially collapsedprior to expansion and radially opened upon balloon expansion. Thesesinusoidal rings are commonly interconnected with a variety of connectordesigns. The connector design either allows stent foreshortening duringexpansion or the connector design allows stent lengthening duringexpansion. For example, when rows of sinusoidal rings are placedpeak-to-peak and a connector joins adjacent peaks of the rows, the stentwill foreshorten during expansion. On the other hand, if the adjacentrings are interconnected with a connector between adjacent valleys, thestent will lengthen during expansion. Thus, additional rows may be addedto produce a stent that lengthens during expansion to compensate forforeshortening around the stent side portion and provides a length inthe range of 10 to 20 millimeters.

FIG. 8 a illustrates additional struts 310 which connect adjacentradially expandable structures 301 so that the stent lengthens duringexpansion, as describe above. FIG. 8 a shows the radially expandablestructures 301 symmetrical on both side of the stent 300. However,either the proximal or distal end may comprise additional radiallyexpandable structures 301 with a strut 310 in between adjacent radiallyexpandable structures 301 to produce varying length stents.Additionally, all of the modifications and variations discussed abovefor other bifurcation stents may be applied to the embodiment of FIG. 8a.

In another embodiment the stent 200 of FIG. 10 has a crimpedconfiguration and an expanded configuration. In the crimpedconfiguration the proximal area of the stent is crimped to a firstdiameter and the distal area of the stent is crimped to a second,smaller diameter. Also, the proximal area of the flaring portion 203 isflush with the stent proximal area and distal area of the flaringportion 203 is also flush with the stent distal area. An example of sucha stent design 200 is shown in FIGS. 10-13, where FIGS. 10-12 shows atwo-dimensional view of the stent 200 and FIG. 13 shows the same stent200 mounted on a balloon 20.

In another embodiment, FIGS. 10-13 describe an example of an ostialstent design 200, similar to the bifurcation design 10 previouslydiscussed. The ostial stent design 200 comprises a structure 201 shownin FIG. 10 which is designed to expand, a connector 202 that connectsbetween the radially expandable structure 201, and an edge portion 203shown in FIG. 11. The radially expandable structure 201 is made ofelements that do not necessarily form a circumferential ring and hang onboth sides of the connector 202. The structure expands to support theside branch vessel while enabling the connector 202 to open.

Connector 202 is designed to have a geometrical preference to deformoutwardly rather than along the balloon surface. Once the expandablestructure 201 expands and allows the connector 202 to open, theconnector 202 is deflected outwardly. The edge portion 203 comprises twowings 204 shown in FIG. 12 that are interconnected with connectingstruts 205. These wings 204 are located on the connectors 202 and aredeployed outwardly into the side branch ostium when the connectors 202deflect. The wings 204 shown in this example are symmetrical althougheach one can have different size or design to allow better support ofdifferent bifurcation angles. An example of an alternate wing designcomprises meandering struts. When the wings 204 are deployed, theconnecting struts 205 are pulled and may provide more coverage to theside branch ostium.

The stent 200 further comprises another radially expandable structure206 shown in FIG. 10 that expands due to inflation of the balloon andsupports the side branch vessel at the stent area close to the ostium.This area of the stent can be designed with many different patterns toallow coverage of the side branch vessel.

In another embodiment the stent may consist an array of connectors 202attached directly to each other without the expandable structure 201. Inthis case the stent 200 may include more then two connectors 202. Thenumber of connectors may be two to six, or more.

FIGS. 14-16 illustrate the process of ostial stent expansion. FIG. 14shows the stent 200 crimped over a balloon 20 in a blood vessel BV whileFIG. 15 shows the stent edge portion 203 deployed after the stent 200has been expanded. FIG. 16 shows the fully expanded stent 200 after theballoon 20 is withdrawn. FIG. 21 shows α, the angle of the flaringportion relative to a central axis of the stent, and is in the rangefrom 10 to 150 degrees. In FIG. 21, the flaring portion is disposed onan end of the stent main body.

In another embodiment the main stent body has a different stiffness nearthe distal end than the area of the stent closer to the ostium. Thisresults in the stent area closer to the ostium to expand first.Deployment of the distal area of the stent and the edge portion can beachieved by altering the design of the balloon to have a larger diameterat the edge portion area. Another example is a thinner balloon wallthickness closer to the edge portion of the stent. This way the edgeportion is pushed against the side branch ostium. Early expansion of thearea near the edge portion pushes the stent into position beforedeploying the stent main body. Balloon distal area design can becontrolled by the wall thickness, mold design or thermal treatments ofthe polymer.

Differences in the radial stiffness in different regions of the stentcan be achieved by various means. One option is to reduce strut width orthickness in the stent area closest to the edge portion. Another optionis to use longer struts where lower stiffness is desired. Anotherpossible way is to increase the spacing between intersecting struts inareas where less radial stiffness is desired.

In one embodiment the edge portion structure is designed to deploy to a90 degree angle. In another variation, the edge portion is designed tobe deployed in various pre-determined angles. Optionally, the edgeportion may be tilted at different angle to accommodate smallbifurcation angle anatomy. An additional way to control the degree offlaring is by applying different inflation pressures to differentsections of the stent with the balloon used for stent expansion.

In another embodiment the stent is symmetrical and both wings 204 of theedge portion 203 deploy the same way and at the same angle.Alternatively the stent may not be symmetrical, thus the distal area ofthe edge portion 203 deploys at a greater angle relative to the proximalarea of the flaring portion. This can be achieved by transmitting lessforce on the connecting strut 202 at the proximal side which in turnwill deflect less and lift the wing 204 to a lesser angle.

An example of a way to transmit less force on the connecting strut 202is to make the radially expandable structure 201 weaker by making theradially expandable structure struts either longer or thinner or both.Similarly, stiffening connecting strut 202 on the distal side transmitsmore force and therefore deflects more thereby lifting the distal wing204 to a greater angle than the proximal wing. Alternatively the wings204 may have different designs to allow for different properties andalso to maximize other benefits such as selective drug delivery forexample. FIGS. 14-16 show the wings 204 opposed to one another. Thenumber of wings can vary from one to eight wings, preferably two to fourwings.

When the side branch take off angle is less then 90 degrees the ostiummorphology is not cylindrically symmetrical as shown in FIGS. 17-19. Inorder to accommodate that morphology the stent 200 may have an angulatedgeometry, meaning that the crimped stent profile is cut at an angle atthe proximal end (FIG. 17). The wings 204 may be gradual andasymmetrical around the stent axis, thus one wing is closer to the stentdistal end than the other. When the stent 200 is deployed in the bloodvessel (BV) with a balloon (20), the wings 204 comply with the ostiumangulation as shown in FIGS. 17-19.

The wings can also differ in length since the distal side of the ostiumis longer than the proximal side. The profile of the distal side of theostium is different than the profile of the proximal side of the ostium.The wings can assume the same or different profiles in order toaccommodate different ostial regions.

FIGS. 22 and 22 a show a bifurcation stent design 10 a. FIG. 22 showsthe bifurcation stent 10 a two-dimensionally, unrolled and flattened.FIGS. 22 a and 22 b respectively show the bifurcation stent 10 a in itsradially expanded configuration in side and perspective views. The stent10 a is generally similar to the stents described above, for example,stents 10 and 300. The stent 10 a comprises a radially expandablestructure 11 and a flaring portion 13. A principal difference betweenthe stent 10 a and the above described stents is that the proximal wing14 a and distal wing 14 b of the flaring portion 13 have differentlengths. As shown in FIGS. 22 and 22 a, the proximal wings 14 a arelonger than the distal wings 14 b.

Stent 10 a further comprises a U-shaped connecter 12 between theradially expandable structure 11 and the flaring portion 13. Stent 10 awill typically have a unitary construction, e.g., the entire stentpattern including the radially expandable structure 11, the connecter12, and the flaring portion 13 may be laser cut from a single tube. Theradially expandable structure 11 is attached to both sides of theconnector 12 but does not necessarily form a circumferential ring. Theradially expandable structure 11 expands to support the main vessel. Theconnector 12 is designed to have a geometrical preference to deformoutwardly rather than along the surface of a balloon used to expand thestructure 11. That is, the struts of connector 12 are sized and arrangedso that connector 12 deforms outwardly in response to a radially outwarddilation force, for example, the expansion of a balloon. The expansionof the structure 11, typically by the expansion of a balloon, will causethe connector 12 to open and deflect outwardly, outwardly deflecting theflaring portion 13 into a side branch vessel. In some instances, theflaring portion 13 may be expanded by a separate balloon inflation fromthat which expands the structure 11. For example, a separate ballooninflation may be used to expand flaring portion 13 if deployment of theradially expandable structure 11 had not caused the plaque underlyingflaring portion 13 to be adequately compressed.

Many prior stent flaring regions, for example, those described in U.S.Pat. Nos. 5,607,444; 5,868,777, PCT Publication Nos. WO 00/44319 and WO03/105695, rely on having weakened or thinner regions which are bent asthe stent is expanded. However, these weakened or thinner regions mayprovide weaker or inadequate support for ostial lesions in bifurcations.The U-shaped connector 12 is instead designed to have a geometricalpreference to deform outwardly rather than along a balloon surface.

The stent 10 a, including the structure 11, the connector 12, and theflaring portion 13, will typically have a uniform thickness. While thethickness and width of the struts of the structure 11 are generallyequal, the width of the connector 12 is designed to be greater than itsthickness. The greater width to thickness ratio increases the moment ofinertia of the connector 12. For example, the width to thickness ratioof the struts of structure 11 may be about 1 (e.g., the struts are about0.1 mm wide and about 0.1 mm thick) while the width to thickness ratioof connector 12 may be about 2.6 (e.g., connector 12 is about 0.26 mmwide and about 0.1 mm thick). Balloon expansion applies a dilation forceon stent 10 a, including the structure 11 and the connector 12.Enlarging the width of connector 12 increases its moment of inertiaalong the balloon surface and thus also its resistance to deformingalong the balloon surface. Generally, the greater the width of connector12, the greater the balloon dilation force required to open theconnector 12. At certain thickness to width ratios, the resistance ofconnector 12 to deform along the balloon surface is greater than theresistance to deform outwardly. Thus, balloon dilation forces will causethe connector 12 to deform outwardly. On the other hand, the connectorsconnecting adjacent struts of the structure 11 lack the requiredthickness to width ratio to deform outwardly and therefore deform alongthe balloon surface.

Flaring portion 13 comprises wings 14 a and 14 b. As shown in FIGS. 22,the proximal wing 14 a and the distal wing 14 b each comprise two wings.However, the proximal wing 14 a and the distal wing 14 b may eachcomprise more than two wings or may each comprise a single wing. Flaringportion 13 may also comprise supporting struts 17 which provide supportto the ostium when expanded. High dilation forces, for example, in theorder of about 10 to 15 atm, may be required to deploy the flaringportion 13 and to overcome plaque resistance in the side branch vesseland ostium. The greater the width of the wings 14 a and 14 b, thegreater their moment of inertia and the greater the dilation forcedistributed to the supporting struts 17. Also, greater widths of thewings 14 a, 14 b can require greater dilation forces for the connector12 to open. Thus, the connector 12 may be designed to distributedilation forces more toward the wings 14 a and 14 b. The connector 12may comprise a twisting portion 12 a and a leg portion 12 b. Thetwisting portion 12 a is positioned near the wings 14 a and 14 b whilethe leg portion 12 b is positioned closer to structure 11. The legportion 12 b may be designed to be wider and/or longer and thus stifferthan the twisting portion 12 a. Thus, outward deformation of theconnector 12 may occur primarily in the twisting portion 12 a. The legportion 12 b also increases the torque applied to open the connector 12,reducing the balloon dilation force needed to open the connector 12.

The size of the connector 12 and its width to thickness ratio areproportional to the dilation force required to expand the flaringportion 13. Thus, the size of connector 12 and its width to thicknessratio can be scaled. For example, if the stent 10 a is designed forsmall side branch vessels and does not include the supporting struts 17,the size of connector 12 and its width to thickness ratio can besmaller. Another example is an ostial stent, such as ostial stent 200,wherein a flaring portion is located at an end of the stent. Such anostial stent may comprise a row of smaller U-shaped connectors, each ofthem deploying a smaller wing and therefore requiring a lesser balloondilation force.

FIG. 23 show the bifurcation stent 10 a expanded into a bifurcation. Themain body of stent 10 a is expanded into main blood vessel BV while thewings 14 a, 14 b are expanded to contact at least the walls of the sidebranch ostium. The bifurcation stent 10 a and the radially expandablestructure 11 define a main body axis 231. When the stent 10 a isexpanded to support vessel BV, the main body axis 231 is parallel to thelongitudinal axis of the main blood vessel BV. The longitudinal axis 232of the side branch vessel SB is also shown in dotted line for ease ofunderstanding. The intersection between the side branch vessel SB andthe main blood vessel BV defines a proximal intersection angle 230 a anda distal intersection angle 230 b. The longer proximal wings 14 a opento an angle 250 which corresponds to the proximal intersection 230 a.

There is also a transition zone or ostium between the side branch vesselSB and main blood vessel BV. This transition zone defines a proximaltransition angle 240 a and a distal transition angle 240 b. The proximaltransition angle 240 a and the distal transition angle 240 brespectively have a proximal and distal radius of curvature. The shorterdistal wings 14 b open to an angle 255 which corresponds to this distalradius of curvature. Typically, the longer proximal wings 14 a will opento a greater angle relative to the main body of the stent 10 a than theshorter distal wings 14 b. For example, as shown in FIG. 23, the longerproximal wings 14 a open to a 130° angle relative to the main body ofthe stent 10 a while the shorter distal wings 14 b open to a 105° anglerelative to the main body of the stent 10 a.

Having the proximal and distal wings 14 a, 14 b of the stent 10 a opento different angles and be of different lengths can have numerousadvantages. When the stent 10 a is expanded into the bifurcation, theproximal wings 14 a and the distal wings 14 b can fit more closely withthe walls of the side branch SB and of the ostium. Also if the distalwings 14 b were longer, e.g., by being the same length as the proximalwings 14 a and extending through dotted line 23 b, the distal wings 14 bmay obstruct blood flow and may limit or prevent access of additionalballoons or stents through the stent 10 a for the treatment of the sidebranch SB.

FIG. 24 illustrates another advantage of having the proximal and distalwings 14 a, 14 b of the stent 10 a open to different angles and be ofdifferent lengths. FIG. 24 shows a side branch stent 240 expanded intothe side branch vessel SB. The side branch stent 240 has a proximal end241 a and a distal end 241 b. The proximal end 241 a can be positionedvery closely to the proximal and distal wings 14 a, 14 b of the stent 10a. This close positioning can minimize the gap between the proximal end241 a of the stent 240 and the proximal and distal wings 14 a, 14 b ofstent 10 a, thus minimizing the chance of restenosis occurringtherebetween. This close positioning can also minimize or evencompletely avoid any overlap between the proximal portion of the sidebranch stent 240 and the proximal and distal wings 14 a, 14 b of thestent 10 a. Any protrusion of the side branch stent 240 into main vesselBV can also be minimized or even completely avoided. Protrusion of theside stent 240 into main vessel BV may limit blood flow in the mainvessel BV and often results in multiple metal layers in the main vessel.These multiple metal layers are prone for thrombosis and may limitfuture access to the side branch vessel SB if reintervention isrequired. The ability to closely position the side branch stent 240 andthe stent 10 a while minimizing gaps and overlap can reduce or evenprevent the occurrence of such problems.

In one embodiment, the stents described herein may comprise radiopaquemarkers similar to 30 in another embodiment, to assist with accuratepositioning of the stent. An example is a radiopaque marker made fromradiopaque material such as gold, platinum, tantalum and the like, thatcan be attached to the stent at different locations and can be viewedvia fluoroscopy. Preferred locations for these radiopaque markers arethe wings 204 of the edge portion. Having radiopaque markers placed oneach of the wings 204 of the flaring portion will assist the physicianin determining where the edge portion 203 is positioned relative to theostium before stent expansion as well as helping to position the stentaccurately. It will also enable the physician to see the edge portion203 deployed over the ostium. This is advantageous because not only doesit help the physician to identify the side branch location but alsohelps in placing a second stent or re-guidewiring the side branch forpost deployment treatments of the side branch area.

The stent can be made from biocompatible alloys such as stainless steel,cobalt chromium, titanium, nickel titanium alloys, niobium alloys or anyother material suitable for use in body implants. The stent may furtherinclude graft materials such as PTFE or polymer membranes. The stent maybe coated with anti-inflammatory drug or other therapeutic agents withor without a polymer. The use of self-expanding materials such as nickeltitanium alloys is optional but not necessary for the functionality ofthe stent and the self-opening of the edge portion. The stent can bemade of resorbable or absorbable materials such as different polymerformulations, magnesium alloys and other materials that are resorbableor absorbable under body conditions.

In one embodiment the stent 200 comprises three sections, a main stentbody, an edge portion 203 and an optional leverage mechanism 202 or 205connecting the main body and edge portion 203. The leverage mechanism202 or 205 is designed to connect the edge 203 portion and the main bodyin a way such that forces and displacement resulting from the partialexpansion of the main body or the inflation of the main body balloon aretransferred and utilized to expand the edge portion 203. Alternativelythe leverage mechanism 202 or 205 can be integrated with the design ofthe edge portion 203 or the main body to help deploy the edge portion203 once the main body balloon is inflated, and can be fabricated in thesame way as the rest of the stent. For example, the entire stent patternincluding the side portion and the leverage mechanism may be laser cutfrom a tube.

In another embodiment of the invention the main body and the edgeportion share the same pattern or same pattern features. These twoportions of the stent are connected by a leverage mechanism withdifferent design features aimed to deploy the edge portion by leveragingthe geometrical changes and forces resulting from the main bodyexpansion.

In an alternative embodiment, the edge portion expansion occurs beforethe completion of the main body expansion. This helps with positioningand alignment of the stent in the bifurcation area, allows the stentsystem to acquire the angle of the bifurcation and helps to comply withthe local anatomy.

Alternatively, in another embodiment the main body of the stent has morethan a single pattern. In this case the area of the stent that is closeto the location of the edge portion has a different pattern than areasof the stent further away from the edge portion. The edge portion mayhave either one of those patterns, a different pattern or no pattern atall.

The stent design allows the use of a delivery system with a singleballoon without the need for additional means for deploying the edgeportion. In this embodiment the profile of the system can be very lowwhen compared to other bifurcation or ostial stent systems and istypically lower than 0.06,″ preferably lower than 0.05″ and usuallylower than 0.04″ which is a typical profile of conventional stents notdedicated to bifurcation or ostial lesions. This low profile can beachieved due to the design of the stent and the automatically deployededge portion.

In further embodiments the stent can be coated with various coatingsincluding biocompatible oxide layer such as Ir oxide and the like, drugcontaining polymer coatings whether biodegradable or not, or drugmolecules, that can help reduce restenosis or minimize inflammations orimpact biological processes in the vessel with a beneficial outcome forthe patient.

In still another embodiment the stent has a crimped configuration and anexpanded configuration. Usually in the crimped configuration the edgeportion is crimped with the stent but is not necessarily flush with thecrimped main body because the struts of the edge portion are notnecessarily flush with the crimped cylindrical stent surface. However,the edge portion may be crimped flush with the main body of the stent.In another variation, the proximal or distal ends of the stent arecrimped to a smaller diameter then the middle area of the stent.

The methods, catheters, and systems of the present invention can beutilized to deliver a wide variety of active substances, including drugsuseful for treating a wide variety of luminal diseases and conditions.The methods and apparatus of the present invention are particularlyuseful for delivering a wide variety of therapeutic and pharmaceuticalagents, referred to collectively herein as active substances,particularly those suitable for treating vascular and other luminalconditions. For example, antiproliferative and antimitotic agents suchas paclitaxel or others, anti-inflammatory agents, immunosuppressiveagents such as sirolimus (rapamycin) or others, antiproliferative andantimitotic antimetabolites such as folic acid analogs and any othertherapeutic agent that can add benefit to the patient. The activesubstance may be provided on or within the stent in a variety of ways.For example, the active substance may be coated over at least a portionof an exposed surface of the stent, typically by dipping, spraying,painting, plasma deposition, electroplating, centrifuge systems or thelike. More typically, however, the active substance may be incorporatedin a polymeric carrier. Suitable polymeric carriers may be resorbable,such as those comprising polylactic acids (PLA), polyglycolic acids(PLG), collagens, and the like. Alternatively, the polymeric carrier maybe a porous but non-resorbable material.

While the above is a complete description of the preferred embodiment ofthe invention, various alternatives, modifications, additions andsubstitutions are possible without departing from the scope thereof,which is defined by the claims.

1. An expandable stent for deployment at a vascular bifurcation having aside vessel branching from a main vessel, the stent comprising: a mainbody for expansion into the main vessel, wherein the main body defines amain body axis; and a flaring portion disposed on a side of the mainbody and adapted to flare radially and offset the main body axis;wherein the flaring portion comprises at least one distal wing and atleast one proximal wing each aligned along the axis of the main body,and wherein the at least one proximal wing is longer than the at leastone distal wing.
 2. The expandable stent of claim 1, wherein the sidevessel branches from the main vessel at an acute angle in a distaldirection.
 3. The expandable stent of claim 1, wherein the at least onedistal wing and the at least one proximal wing are configured to open atdifferent angles relative to the axis of the main body when the flaringportion flares radially into the side branch vessel.
 4. The expandablestent of claim 4, wherein the at least one proximal wing is configuredto open to a greater angle relative to the main body than the at leastone distal wing.
 5. The expandable stent of claim 1, wherein the flaringportion is adapted to flare radially and offset the main body axis inresponse to expansion of the main body into the main vessel.
 6. Theexpandable stent of claim 5, further comprising at least one connectordisposed between the main body and the wings, wherein the at least oneconnector deforms in response to expansion of the main body to cause thewings to flare radially.
 7. The expandable stent of claim 6, wherein theat least one distal wing and the at least one proximal wing eachcomprise a base and sides, and wherein the at least one connector isdisposed between the main body and the base of each wing.
 8. Theexpandable stent of claim 7, wherein the at least one connectortransfers displacement and expansion forces from the main body to theflaring portion during expansion of the main body.
 9. The expandablestent of claim 1, wherein the at least one distal wing consists only ofone distal wing.
 10. The expandable stent of claim 1, wherein the atleast one proximal wing consists only of one proximal wing.
 11. Theexpandable stent of claim 1, wherein the at least one distal wing andthe at least one proximal wing each comprise a base, sides, and aradiopaque marker disposed above the base and between the sides.
 12. Theexpandable stent of claim 1, wherein the at least one distal wing andthe at least one proximal wing each comprise a base, sides, and strutsextending from the sides of each wing to the main body to providecoverage of a side branch ostium when the wing is opened into saidostium.
 13. The expandable stent of claim 1, wherein the expandablestent is balloon expandable.
 14. The expandable stent of claim 1,wherein the flaring portion flares at an angle in the range from 10 to150 degrees relative to the main body axis when the main body isexpanded.
 15. The expandable stent of claim 1, further comprising atherapeutic agent disposed over at least a portion of the expandablestent.
 16. The expandable stent of claim 15, further comprising apolymeric layer, wherein the therapeutic agent is sequestered in thepolymeric layer.
 17. A stent delivery system comprising: an expandablestent as in claim 1; and a delivery catheter comprising: (a) a shafthaving a proximal end and a distal end; and (b) an inflatable balloondisposed near the distal end of the shaft; wherein the stent is disposedon the balloon with the distal end of the stent faced distally and aproximal end of the stent facing proximally.
 18. A method for deployinga stent at a vascular bifurcation having a side vessel branching from amain vessel, said method comprising: positioning a main body of thestent in the main vessel at the bifurcation; opening a distal wing and aproximal wing from the main body into the side vessel, wherein thedistal wing is shorter than the proximal wing so that there is greatercoverage on a proximal surface of the side vessel by the proximal wingthan on the distal surface of the side vessel by the distal wing. 19.The method of claim 18, wherein the side branch branches from the mainvessel at an acute angle in a distal direction.
 20. The method of claim18, wherein the vascular bifurcation defines a proximal intersectionangle between the main vessel and the side vessel, and wherein openingthe proximal wing comprises opening the proximal wing to an anglecorresponding to the proximal intersection angle.
 21. The method ofclaim 18, wherein the vascular bifurcation defines a transition zonebetween the main vessel and the side vessel, the transition zone havinga distal radius of curvature, and wherein opening the distal wingcomprises opening the distal wing to an angle corresponding to thedistal radius of curvature.
 22. The method of claim 18, furthercomprising: positioning a side branch stent at the side vessel, whereinthe side branch stent has a proximal end and a distal end and whereinthe proximal end of the side branch stent is positioned adjacent thebifurcation; expanding the side branch stent, wherein the greatercoverage on the proximal side of the side vessel by the proximal wingthan on the distal side of the side vessel of by the distal wingminimizes the gap between the proximal end of the side branch stent andthe proximal and distal wings of the main body.